With the increase of concerns about insufficient crude oil and climate change attributable to carbon dioxide emission, attempts to use renewable energy sources have been increasingly made. Particularly, the production of a fuel for transportation using biomass, which is a renewable energy source obtained from biological organisms, has attracted considerable attention.
Biodiesel is a typical fuel used for producing power for transportation. Biodiesel is produced in the form of a fatty acid methyl ester (R1—COO—R2, R1: an alkyl group of fatty acid, R2: a methyl group) by the transesterification reaction of a triglyceride and methanol as raw materials. Most triglycerides are vegetable oils obtained from beans, rapeseed, sunflower seeds, and the like.
When the biodiesel produced in this way is used as a fuel, the biodiesel is helpful to the reduction of carbon dioxide emissions because it is carbon-neutral. However, the biodiesel is problematic in that it is difficult to use in a low-temperature climate region because it has low fluidity at a low temperature, and in that it corrodes an internal combustion engine and is difficult to store for a long time.
In order to solve such problems of biodiesel, hydrodeoxygenation (HDO) has been researched. According to a document (reference: G. W. Huber et al., Applied Catalysis A: General 329 (2007) 120-129), the hydrodeoxygenation of biodiesel was tested based on a hydrodesulfurization catalyst and a hydrodesulfurization apparatus, and, as a result, oxygen included in a triglyceride (raw material) was removed in the form of water (H2O), carbon dioxide (CO2) or carbon monoxide (CO), thus producing hydrocarbons. However, considering the reaction conditions mentioned in this document, it is determined that high process pressure is required and a large amount of hydrogen is used, so it is predicted that operation costs and equipment costs will be increased.
In order to solve the above problem, recently, patents of Neste Oil Company (EP 1681337, KR 10-2007-0094913(A)) and several theses (I. Kubickova et al., Catalysis Today 106 (2005) 197-200, and I. Simakova et al., Applied Catalysis A: General 355 (2009) 100-108) have disclosed methods of removing oxygen from a triglyceride in the form of carbon dioxide or carbon monoxide using active carbon supported with palladium or platinum, and simultaneously reducing the consumption of hydrogen compared to the consumption of hydrogen in the hydrodesulfurization process. However, the methods disclosed in the above patents and theses are also problematic in that, although the consumption of hydrogen is greatly reduced, operation costs and equipment costs are also high because hydrogen is still used.
That is, there is a problem in that, when a conventional catalyst supported with a noble metal is used, oxygen is removed from the triglyceride at relatively low temperature in the form of carbon dioxide or carbon monoxide by a decarboxylation or decarbonylation reaction, but the catalyst is expensive, and hydrogen must be used in order to stabilize the catalyst.